Corrections spending now eats up about 25 percent of the general fund, compared to about 20 percent in 2000.

But Alabama's prison population hasn't been growing near as quickly. Over that same time frame, the number of criminals incarcerated in Alabama is up by just 15 percent, from roughly 22,000 to just over 25,000. And the figure is essentially flat since 2009.

That's not to say Alabama's prisons aren't overcrowded. Since 2000, the state's prisons have been about 90 percent over capacity on average, with about 24,600 prisoners being housed in buildings designed for a combined capacity of about 13,000. In a radio invterview on Tuesday, Gov. Robert Bentley said he would support building additional prisons if he were to win a second term.

But while overcrowding has been a problem for more than a decade, the problem isn't necessarily worsening. The state's prison overcrowding index -- prisoners as a percent of capacity -- was 189 percent in January 2013, compared to 193 percent in January 2002.

So if the prison population isn't growing all that quickly, what's behind rising costs? A closer look at the Department of Corrections' spending over time is needed, but one factor may be medical care.

In 2007, the Alabama Department of Corrections spent $102.1 million on medical and other professional services, its annual report shows. Five years later, that amount had increased to $118.3 million -- a jump of $16.2 million, or 15.8 percent. Over that same time frame, personnel costs grew by less than $10 million, or 5.8 percent.

The Department of Corrections' total spending in the 2012 fiscal year was $437.3 million, compared to $378.0 million in 2007.